Main Rheological Models

The first example shows the influence of dampers on dynamic characteristics of structure. The main objective of the second example is to show that dynamic characteristics of a structure with dampers, modelled using two different rheological models of dampers is practically identical if both models have approximately equal possibilities to dissipate energy. A frame very similar to the one analyzed in Example 1 is considered in Example 3. However, the structure is now analyzed in a time domain and the optimal location of dampers... 

Nevertheless the main difficulty of the oscillating tip results concerns an accurate description of the viscoelastic response of the nanoprotuberance under the action of the attractive force between the sample and the tip. Many points remain open for the interpretation of the atypical variations of the amplitude. They are mostly linked to the multiple crude assumptions made with the model it is difncult to evaluate a local response when both the tip shape and effective force are unknown. One could discuss for example the sphere-plane surface interaction used, or ask about the local stiffness of the polymer, or question the unique relaxation time which is a to simple polymer viscoelastic response. Among our fit parameters, the sample properties should be independent of the drive amplitudes used. The variations reported in figure 15 indicate that a simple rheological model is unable unable to describe the whole growth process of the nanoprotuberances. 

A transient numerical analysis has been carried out of the EHL shut-down conditions examined experimentally by Glovnea and Spikes [1]. The main features of the experimental measurements are reproduced in the numerical results obtained. There are differences observed in the detailed comparison of film thickness profiles. These may be the result of the particular form of non-Newtonian rheological model adopted for the numerical analysis. If so, such comparisons may be a means of distinguishing between such models within an EHL contact. 

Unlike traditional textbooks of tribology, in this book we regard boundary lubrication as a limit state of hydrodynamic lubrication when film thickness is down to molecular dimension and independent of the velocity of relative motion. The discussions are based on the existing results, some from literatures but mostly from the authors own work. The topics are mainly focused on the mechanical properties of boundary films, including rheology transitions, molecular ordering, and shear responses. Ordered molecule films, such as L-B films and SAM, are discussed, with emphasis on the frictional performance, energy dissipation and the effects from structural features. Boundary films can be modeled either as a confined substance, or an adsorbed/reacted layer on the... 

Polymer silicate nanocomposites offer unique possibilities as model systems to study confined polymers or polymer brushes. The main advantages of these systems are (a) the structure and dynamics of nanoconfined polymer chains can be conveniently probed by conventional analytical techniques (such as scattering, DSC, NMR, dielectric spectroscopy, melt rheology) (b) a wide range of different polymers can be inserted in the interlayer or end-grafted to the silicate... 

In summary, the QCM-D technique has successfully demonstrated the adsorption of pectin on the BSA surface as well as determined the viscoelastic properties of the pectin layer. As pectin concentrations increase, the adsorbed mass of pectin estimated from the Voigt model show higher values than those estimated from the Sau-erbrey equation because the former takes into account the hydrated layer. But the similar increase of thickness of pectin suggests that the pectin chains form a multilayer structure. In agreement with our previous rheology results, the main elastic character of the pectin layer in terms of Q-tool software tells us the network structure of the pectin layer on the BSA surface. In summary, QCM-D cannot only help to better understand the polysaccharide/protein interactions at the interface, but also to gain information of the nanoscale structure of polysaccharide multilayers on protein surface. 

Poly(methylmethacrylate), PMMA, latex particles have also served as a model colloidal system for many years (mainly as hard spheres with hydroxy stearic acid (HSA) chains being the grafting choice [91,113,114]). Tunability was achieved by varying the core size and the size of the corona chains. The comparison between chemically grafted (stable) and end-adsorbed temperature-sensitive chains (usually surfactants) has shown that the adsorbed chain particles exhibit similar rheological behavior with chemically grafted particles [115]. 

The applied stress results in the shear strain of the cube, i.e. the top face becomes shifted with respect to the bottom one by distance y. This displacement is numerically equal to the tangent of a tilt angle of the side face, i.e. it is equal to the relative shear strain, y, and at small strains tany y. The relationship between shear stress, x, and shear strain, y, and the rates of change in these quantities with time, dx/dt=x, dy/dt=y, represent mechanical behavior, which is the main subject in rheology. One usually begins the description of mechanical behavior with three elementary models, namely elastic, viscous, and plastic behavior. 

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